Low-temperature formation of Ce-based fluorite-type multicomponent (RE)O2-δ oxides via freeze-dried precursor

Accessing compositionally complex rare-earth fluorite oxides usually requires high thermal budgets to ensure cation homogenization and phase purity. Here, it is demonstrated that a freeze-dried precursor–based synthesis provides an energy-efficient pathway to stabilize multication fluorite solid solutions under unusually mild conditions. Freeze-dried amorphous precursors are converted into single-phase cubic fluorite (Fm3̅m) oxides at temperatures as low as 500 °C across a systematic compositional series ranging from binary (CePr)O 2-δ to six-component (CePrLaNdYSm)O 2-δ . Phase purity is maintained up to 800 °C, while secondary phases emerge at higher temperatures, indicating the limits of entropy-assisted stabilization. Structural trends indicate temperature-controlled crystallite growth and a pronounced La³⁺-induced lattice expansion, whereas increasing lattice disorder and defect signatures with compositional complexity are evidenced by Raman and optical analyses. Overall, freeze-dried precursor–based synthesis enables low-temperature access to rare-earth high-entropy fluorite oxides, offering a versatile platform for defect-tolerant and nanostructured functional materials.